GRT & eGWM Migration reducing amplitude risk to get accurate

elastic attributes

SPE2019 conference

14th May 2019Jagat Deo

MIGRATION definition

• Generalised Radon Transform (GRT)

– This fully preserves amplitudes since it’s a multi-arrival solution

outputting data in the angle domain. Amplitudes at the incidence

angle are proportional to the reflection coefficient and thus ideal

for elastic work.

• eGWM (Guided Wave migration)

– Fully supports amplitude integrity and produces higher quality

inversions than from Kirchhoff. It outputs offset and angle

gathers for velocity updating and Pre-Stack elastic inversion cost

effectively. 1/30 compute cost of RTM.

Rosebank Intra-Basalt Imaging Legacy Streamer(1997) vs OBN (2016)

NOTE: Same velocity model is used as derived from the OBN

1. Legacy Kirchhoff vs GRT Streamer

2. OBN RTM

2019 GRT Broadband

Reprocessing legacy streamer with high end code produce data similar to OBN 2016 survey >>>

2007 3D Kirchhoff LEGACY

BASALT Layer Colsay-1

Colsay-3

Colsay-1

Colsay-3

GRT Final Stack in Time OBN RTM(50Hz) Stack in Time

RTM amplitudes not preserved or tie the synthetics. Any Brightening is not GAS related

Amplitude Tie CDP syntheticCorrect elastic attributes

GRT migration high resolution – Angle gathers for accurate elastic fields >>

Colsay-5?

LMR “probably” related to fluid

GRT Final Stack Lambda-Rho from Three GRT angle stacks + InvQ

Is this a Eureka moment?

Kirchhoff Gathers (offset)

Critical energy offsets ~ 2800m

Kirchhoff Gathers Angles

GRT Gathers Angles

0-5deg missing. Critical angles smeared beyond 45deg Useable angles up to 36deg

Residual critical energy is at the wrong angle and is often mistaken as far angle AVO

Critical energy is at the correct angle and accurate AVO is now obtained

Kirchhoff has RISK of FALSE AVO

EnochDu & Finlaggan Block 21/5

21/5-6 Enochdhu: Lambda-Rho Kirchhoff

21/5-6 Enochdhu

21/5-6 Enochdhu: Lambda-Rho GRT

21/5-6 Enochdhu

Missed pay

GRT highlights missed pay

eGWM

One-Way wave equation using guided waves

Elastic wavefields to generate synthetic shots

Pwave Swave density

Fluid responseFluid response

Gather locations

eGWM (TS Imaging) vs Kirchhoff offset gathers in depth

eGWM Kirchhoff

Top: Class-3Base: Class-2P

Top: Class-3Base: Class-2P

Marmousi Velocity Model

Marmousi: Kirchhoff (Cannot handle complexity FWI

models)

Marmousi: eGWM No Mute Energy in Evanescent zone is

not in the image) Marmousi Velocity Model

Remarks

• Applying advanced algorithms on legacy data (Broadband –ePEG – GRT) has extracted possible fluid signature for the first time in the Rosebank Colsay sands! Derisking future Sub-Basalt Imaging plays. GRT is preferred over Kirchhoff.

• eGWM is a new low cost effective alternative for one-way wave equation solution and outputs gathers for inversion. Attenuates noise in the imaging condition. eGWM has several advantages over RTM.

Acknowledgments

• Zennor Petroleum UK Ltd

• Suncor UK Ltd, Siccar Point UK, Equinor Norge